Commercial Air Tightness Testing
Compliance for Non-Domestic Buildings
Commercial Air Tightness Testing — Part L2 Compliance for Non-Domestic Buildings
Commercial air tightness testing is a mandatory requirement under Part L2A of the Building Regulations for all new non-domestic buildings in England and Wales. Without a compliant air permeability test result, the SBEM assessor cannot complete the as-built non-domestic EPC, and without the as-built EPC, building control cannot issue the completion certificate. For commercial developers, investors, and contractors, a failed or delayed air tightness test represents a direct threat to practical completion and handover and the financial consequences in a commercial development context can be substantial.
Stansted Environmental Services Ltd provides commercial air tightness testing through ATTMA Level 2-registered testers who are experienced in testing offices, retail units, schools, healthcare buildings, warehouses, industrial units, mixed-use schemes, and other non-domestic building types across the United Kingdom. We plan our tests carefully, use the right equipment for the building size, and produce reports that your SBEM assessor can use immediately.
What Is Commercial Air Tightness Testing?
Commercial air tightness testing follows the same fundamental principle as residential testing, a calibrated blower door fan is used to pressurise or depressurise the building to a reference pressure of 50 Pascals, and the airflow through the fan at each pressure step is measured to calculate the air permeability of the building envelope. The result is expressed in m³/h/m² @ 50 Pa and compared against the design air permeability target established in the SBEM calculation prepared by the building’s SBEM assessor.
The key difference between commercial and residential testing is scale. Large commercial buildings, offices, distribution centres, retail parks, schools have envelope areas that a single blower door fan may not be able to pressurise to the required pressure differential. For these buildings, multiple fans are used simultaneously in a fan array configuration, with the combined flow capacity sufficient to achieve the test pressure across the full envelope area. SES has the equipment and the methodology to test commercial buildings of all sizes, from a single-storey retail unit to a multi-storey office complex with thousands of square metres of treated floor area.
When Is Commercial Air Tightness Testing Required?
Commercial air tightness testing is required under Part L2A for all new non-domestic buildings where the treated floor area exceeds 500 m², and is strongly recommended for smaller non-domestic buildings where the SBEM assessor has used a design air permeability figure better than the default value of 10.0 m³/h/m² @ 50 Pa. It is also required for certain conversions and change-of-use projects where the SBEM calculation needs to demonstrate compliance with the energy requirements of Part L2B.
Building control bodies routinely require evidence of a commercial air tightness test as part of the completion application package, and many planning authorities in London and other major cities also reference air permeability targets in energy-related planning conditions that must be discharged before occupation. If you are unsure whether commercial air tightness testing is required for your specific development, SES can review your building control application, SBEM assessment, and planning conditions and advise you definitively.
Shell and Core Testing for Speculative Commercial Developments
Many commercial developments are delivered in two distinct stages. The shell and core stage covers the construction of the structural frame, external envelope, roof, primary mechanical and electrical infrastructure, and common areas, but excludes the tenant fit-out of individual lettable units. The post-fit-out stage covers the full completion of the building following tenant fitout, including all internal partitions, floor finishes, ceilings, and secondary mechanical and electrical services.
Commercial air tightness testing can be carried out at both stages. At shell and core stage, a test is conducted on the completed envelope and a non-compliance certificate is generated that records the shell and core air permeability result. This satisfies building control at that stage of the works without requiring the fit-out to be complete. Following fit-out completion, a further test is carried out and the as-built result — which should be equal to or better than the shell and core result — is used by the SBEM assessor to produce the final compliance certificate and lodge the as-built non-domestic EPC. This approach is standard practice on speculative commercial schemes and is well understood by building control officers in all major regional markets.
What Happens If the Commercial Test Fails?
A commercial air tightness test result that exceeds the design target will require the SBEM assessor to update the as-built calculation using the actual result. Whether the building still demonstrates compliance with Part L2A depends on how much worse the actual result is than the design figure and how much headroom existed between the calculated building emission rate and the target. If the updated calculation no longer demonstrates compliance, additional fabric improvements or mechanical and electrical upgrades will be required before the building control application can be completed.
Identifying the sources of air leakage in a commercial building and remediating them before retesting is more complex than in a residential building, due to the larger envelope area and the number and variety of penetrations, interfaces, and services that need to be checked. However, the most common leakage paths in commercial buildings include service penetrations through roof decks and external walls, interfaces between curtain walling and structural edge beams, expansion joints, poorly sealed rooflight surrounds, and incomplete sealing at the perimeters of cladding panels are well documented and can usually be addressed systematically within a reasonable programme period. SES can assist in identifying and locating leakage paths during a diagnostic pressurisation visit and can advise on the remedial approach.
ATTMA Level 2 Registration and What It Means
ATTMA Level 2 registration covers air tightness testing of non-domestic buildings of all sizes and types, and is the Authorised Competent Persons Scheme for commercial air tightness testing listed in the Building Regulations. SES holds Level 2 registration, which means our commercial test results are automatically accepted by building control bodies without the need for additional verification. Our testers are trained and assessed to the standards set out in ATTMA Technical Standard L2 and CIBSE TM23, and our testing equipment is maintained and calibrated in accordance with the requirements of those standards.
The distinction between Level 1 (domestic) and Level 2 (non-domestic) registration is important. Some air tightness testing companies hold only Level 1 registration and are not authorised to test non-domestic buildings. Using an unregistered tester for a commercial building can result in building control refusing to accept the test result, requiring a retest by an ATTMA Level 2-registered organisation at additional cost and programme delay. Always confirm that your air tightness tester holds the appropriate ATTMA registration before instructing them.
How Much Does Commercial Air Tightness Testing Cost?
Commercial air tightness testing is priced based on the treated floor area of the building, the number and size of fans required to achieve the test pressure, access conditions, and travel distance. For a single-storey commercial unit of around 500 m² treated floor area in the South East of England, commercial air tightness testing typically starts from around £600 to plus VAT. Larger buildings requiring multi-fan configurations are priced accordingly, and we provide a fixed-price quotation for each project based on the SBEM assessment drawings and specification.
As with residential testing, the cost of the test is small relative to the cost of a failed result that delays completion. A commercial building that cannot achieve its SBEM compliance target because of poor air tightness performance may require expensive mechanical upgrades, enhanced heat recovery ventilation, for example, or additional insulation to compensate for the envelope performance shortfall. Getting the air tightness right is far cheaper than fixing the SBEM calculation after the fact.
SES are a multi-disciplined environmental consultancy with a proven track record of providing high quality.
Commercial Air Tightness Testing Across the UK
SES provides commercial air tightness testing in London and across the South East, including Essex, Kent, Surrey, and Hertfordshire, as well as in the Midlands, the North West, Yorkshire, East Anglia, and all other regions of England and Wales. We work regularly with national and regional developers, principal contractors, M&E contractors, and SBEM assessors on commercial schemes of all types and sizes.
Request a Commercial Air Tightness Testing Quote
Contact SES on 0808 239 2327 or 020 3993 4974, or complete our online enquiry form. Please provide the site address, the treated floor area and building type, the SBEM design air permeability target, and your preferred testing window, and we will provide a fixed-price quotation and availability confirmation promptly.
